The major objectives of this project are to study immunological mechanisms of host defenses against acute, persistent, and latent viral infections. Systemic and local defenses are being investigated with reference to both specific and nonspecific immune mechanisms. In particular, the mutual interaction of antibody, lymphocytes, macrophages, and mediators are being examined to ascertain their various roles in the process of recovery from disease. Projects of present interest are: 1) the effect of tuberculin delayed-type hypersensitivity reactions on vaccinia virus infections in rabbit skin; 2) the effect of Mycobacterial and mycobacteria cell products on vaccinia virus infections in rabbit skin and systemic encephalomyocarditis virus and HSV-II infections of mice; and 3) the effect of previous virus infections on superinfection with an unrelated virus.